The type-I seesaw mechanism for light neutrino masses, popularly known as
canonical seesaw was originally proposed by [1]}, [2]}, [3]}, [4]}. It is the simplest
mechanism that explains the lightness of SM neutrino masses with the
introduction of heavy right-handed neutrinos. The right-handed neutrinos being
singlet under SM, are used to write down a Dirac mass term between SM neutrinos
\(\nu _L\)  and right-handed neutrinos \(N_R\)  along with a bare Majorana mass term
for right-handed neutrinos \(N_R\) .
